"We are both so busy that we have people helping us with the plans," Lambert tells PEOPLE. "I am just trying to enjoy being engaged. It's kind of a magical time."
For his part, Shelton feels that a weight's been lifted. "The beatings from her are less severe and less frequent now that I've stepped up, so that's been a good thing," he says, joking. "I feel like I can relax. Every time she has an idea for the wedding that she tells me about, I tell her it's the same thing I was thinking. It's all good."
Shelton, 34 , proposed to Lambert, 26, on May 9. It happened to be Mother's Day and one of those rare quiet times for the busy couple.
"She and I were going to be home for about three days together, just the two of us, and that doesn't happen that often," Shelton says. "I wanted to ask her on that first day she got home, so we'd have a couple of days together, just alone."
"I had just come off the road, and we had the afternoon together, and it was a complete surprise," says Lambert, adding that it was low-key and romantic. "It was us two in the woods in Oklahoma … It wasn't one of those fancy dinners where you get all fancied up."
A "Vintage" Ring
The couple had looked at rings together, but Shelton was drawn to something else – and Lambert quickly fell in love with it, too.
"It's absolutely beautiful," she says of the ring. "It has a vintage feel, and that's one thing I always wanted. It's platinum and has a big stone in the middle and two half-moon stones on the side."
They've said the wedding will be next spring, and while they're just starting to plan, one element will obviously be non-negotiable. "The only must-have for me is country music," Shelton says. "And I know it won't get any argument from her."
But rings and ceremonies are secondary to the real reason for celebration: that after five years of a relationship that's had its ups and down, they've taken that next step toward committing their lives to each other.
"I feel mostly happy because I'm really, truly in love with the person I'm engaged to," says Lambert.
Adds Shelton: "We've been together long enough to know that we're more miserable apart than we are together. I think we're meant to be together, so we're just going to do something about it – finally!"
Reporting by DANIELLE ANDERSON, EILEEN FINAN and KAY WEST
Read more about Blake and Miranda's engagement in the new issue of PEOPLE Country, on newsstands Friday, and download free music from other hot country artists